1. Field of the Invention
The present invention relates to a cellular telephone set, and more particularly to a cellular telephone set which is capable of receiving a plurality of broadcast waves including TV and FM broadcast waves in UHF and VHF bands.
2. Description of the Related Art
For radio units and receivers that are commercially available today to be compatible with frequencies in the VHF band for FM and TV broadcast waves and with frequencies in the UHF band for TV broadcast waves, the radio units and receivers often use a rod antenna, a helical antenna, or the like because wavelengths in the VHF band for TV broadcast waves are very long. Heretofore, various arrangements, to be described below, available to adjust radio waves that are received by a single antenna, depending on the situation in which the radio waves are used.
Japanese laid-open patent publication No. 2000-156651 discloses a communication terminal having a TDMA radio unit and a CDMA radio unit which share a single antenna, the radio units being selectively switched to use the antenna.
Japanese laid-open patent publication No. 2001-077719 reveals a cellular telephone set having a plurality of impedance adjusting circuits for handling an impedance change caused when the cellular telephone set is close to or contacts a human body, and a switch for selecting one of the impedance adjusting circuits to be used depending on whether there is an audio signal or not.
Japanese laid-open patent publication No. H03-192902 discloses an antenna device having an antenna shared by an automobile radio telephone set and an AM/FM receiver, and an impedance converter circuit for AM broadcasts and a matching circuit for FM broadcasts which are connected between the antenna and the AM/FM receiver.
The VHF and UHF bands for FM and TV broadcasts are very wide, and it is difficult for the antennas of small-size radio units to simultaneously satisfy antenna characteristics for both VHF and UHF bands.
If a cellular telephone set has the additional function of receiving FM and TV broadcasts, then the cell phone's antenna is used to share receipt of both FM and TV broadcast signals. However, it is possible that the shared antenna system may effect the radio circuits which receive both telephone and broadcast signals.
The communication terminal disclosed in Japanese laid-open patent publication No. 2000-156651 simplifies switching between the receiver circuits, but does not addresse the problems described above.
The cellular telephone set disclosed in Japanese laid-open patent publication No. 2001-077719 selects one of the impedance adjusting circuits depending on whether the cellular telephone set is close to or contacts the human body. However, the above problems cannot be solved by the disclosed cellular telephone set.
The antenna device disclosed in Japanese laid-open patent publication No. H03-192902 has an impedance converter circuit for AM broadcasts and a matching circuit for FM broadcasts which are connected between the antenna and the AM/FM receiver. If the disclosed antenna device is applied to a wide band such as a VHF or UHF band for FM and TV broadcasts, then the arrangement of a network for implementing the impedance converter circuit and the matching circuit becomes complex in arrangement, and is difficult to realize.